1. Field of the Invention
This invention relates to an idling speed control system for an outboard motor, particularly to an idling speed control system for an outboard motor for small boats
2. Description of the Related Art
Small motor-driven boats are generally equipped with a propulsion unit including an internal combustion engine, propeller shaft and propeller integrated into what is called an outboard motor or engine. The outboard motor is mounted on the outside of the boat and the output of the engine is transmitted to the propeller through a clutch and the propeller shaft. The boat can be propelled forward or backward by moving the clutch from Neutral to Forward or Reverse position.
The idling speed of this type of the engine is controlled by use of a secondary air supplier that supplies secondary air through a passage that is connected to the air intake pipe downstream of the throttle valve. The passage is equipped with a secondary air control valve and the desired idling speed is obtained by regulating the opening of the secondary air control valve.
The amount of secondary air required to achieve the desired idling speed varies with aged deterioration of the engine. It also differs with clutch position. This is because the idling speed differs between that when the clutch is in Neutral and that when it is in Forward or Reverse and the outboard engine is running forward or backward at very low speed, i.e., during trolling.
To give a specific example, say that the idling speed is 750 rpm when the clutch is in Neutral. When the clutch is then shifted into Forward or Reverse for low-speed trolling, the added load of the hull causes the engine speed to fall to the trolling speed (herein defined as the idling speed during trolling) of around 650 rpm. The required amount of secondary air changes as a result.
If the owner of the outboard motor should replace the propeller, which is not uncommon, the resulting load change will change the engine speed and, accordingly, change the amount of secondary air required to achieve the desired idling speed. Conventional idling speed control does not take clutch position and propeller replacement into account and stands in need of improvement in this respect.
An object of the present invention is therefore to achieve this improvement by providing an idling speed control system for an outboard motor that is equipped with an internal combustion engine responsive to shifting of a clutch from Neutral to Forward or Reverse for driving a boat forward or backward according to the clutch position after shifting and that supplies secondary air in such amount as to reduce deviation between a determined desired idling speed and a detected engine speed, which idling speed control system for an outboard motor accurately determines a desired idling speed and a desired amount of supplied secondary air so as to achieve steady idling even when load varies owing to operation (shifting) of the clutch or propeller replacement.
For realizing this object, a first aspect of this invention provides a system for controlling an idling speed for an outboard motor mounted on a boat and equipped with the engine whose output is connected to a propeller through a clutch such that the boat is propelled forward or reverse when the clutch is changed to a neutral position to a forward position or a reverse position, having: secondary air supplier that supplies secondary air trough a passage that is connected to an air intake pipe downstream of a throttle valve and that is equipped with a secondary air control valve such that amount of secondary air is supplied to the air intake pipe in response to an opening of the secondary air control valve; engine operating condition detecting means for detecting parameters indicative of operating conditions of the engine including at least an engine speed; engine start-state determining means for determining engine start-state as to whether the engine has been started based on one of the detected parameters; desired value determining means for determining a desired idling speed and for determining a desired secondary air supply amount such that a deviation between the determined desired idling speed and the detected engine speed decreases; and valve controlling means for controlling the opening of the valve to a value that effects the desired secondary air supply amount; wherein the improvement comprising: the system includes: clutch position detecting means for detecting the position of the clutch; and wherein the desired value determining means determines the desired idling speed and the desired secondary air supply amount based on the determined engine start-state and the detected clutch position. With this, the system can therefore accurately determine the desired idling speed and the desired secondary air supply amount and achieve steady idling speed even if load changes owing to a change in clutch position or propeller replacement.
In accordance with a second aspect of the invention, the desired value determining means learning-controls the determined desired secondary air supply amount. With this, the system can also accurately determine the desired idling speed and the desired amount of supplied secondary air and achieve steady idling speed even if load changes owing to a change in clutch position or propeller replacement.
In accordance with a third aspect, the desired value determining means learning-controls the determined desired secondary air supply amount such that the deviation between the desired idling speed and the detected engine speed decreases. With this, the system can therefore achieve steady idling speed even if load changes owing to a change in clutch position or propeller replacement and, in addition, by enabling steady low engine speed during slow advance with the clutch shifted to Forward (or Reverse) position can enhance fuel performance.
In accordance with a fourth aspect, the desired value determining means determines to correct the desired secondary air supply amount by a prescribed amount such that the deviation between the desired idling speed and the detected engine speed decreases, when the clutch position is shifted or changed. With this, the system can similarly achieve the same results mentioned above.